The effect of titania content on the refractive index of titania/polyimide composite films prepared by the sol-gel process

Titania/polyimide composite films were fabricated from a polyamic acid of pyromellitic dianhydride (PMDA)/4,4'-oxydianiline (ODA) as a polyimide precursor and titanium n-butoxide by the sol-gel process. The ratio of titania weight to the combined weight of polyamic acid and titania, W, was up to 0.4, assuming complete conversion of titanum n-butoxide to titania. Refractive index dispersions and extinction coefficients of the prepared films were measured in the wavelength range from 400 to 800 nm by ellipsometer. Refractive index at a wavelength of 633 nm was increased from 1.67 for a pure polyimide to 1.77 for the titania/polyimide composite film at W=0.4.